Peugeot used an internally filleted brazing approach, rings of brazing rod formed to mimic the joint, set inside the tube. Heat it up and when ready, internal fillet with just a hint of brazing material around the exterior.
They were quite proud of the process, but it had too much association visually what came from AMF and the like.
John Jorgensen Palos Verdes Ca USA
Only real Confentes around here.